<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <style>
      .san {
        width: 0;
        height: 0;
        border-left: 50px solid transparent;
        border-right: 50px solid transparent;
        border-bottom: 100px solid red;
      }

      .san1 {
        width: 0;
        height: 0;
        border-left: 50px solid transparent;
        border-right: 50px solid transparent;
        border-bottom: 100px solid red;
        transform: rotate(180deg); /* 旋转 180 度 */
      }
    </style>
  </head>
  <body>
    <div class="san"></div>
    <hr />
    <div class="san1"></div>
  </body>
</html>
